Thermostatic shower mixers - what do you gain by paying more?

[Dave]

I'm astonished by the price range of thermostatic shower mixers; £70 up to many many hundreds. Surely a mixer is just a metal casting, a wax capsule and a tap; what do you get if you pay more?

[Andrew Gabriel]

I've noticed they seem to be about 1/4 of the price in France for what appear to be the same models, although I haven't extensively researched this -- just happened to notice this in a French store shortly after buying one in the UK.